Apparatus for pumping a high pressure laser system

ABSTRACT

An apparatus for optically pumping a transversely excited, high pressure gaseous laser system by means of a double electrical discharge using a capacitor-bank network and electronic circuitry for implementing the method. Laser energy pulse outputs of approximately 17 Joules/liter at efficiencies of 24% have been obtained by the inventive concept.

United States Patent 9] Pan et al.

[ Mar. 5, 1974 APPARATUS FOR PUMPING A HIGH PRESSURE LASER SYSTEM [75]Inventors: Yu-Li Pan, Oakland; Anthony F.

Bernhardt, Piedmont; Joe R. Simpson, Dublin, all of Calif.

[73] Assignee: The United States of America as represented by the UnitedStates Atomic Energy Commission, Washington, DC.

[22] Filed: Nov. 3, 1372 [21] App]. No.: 303,553

[52] US. Cl. 331/945, 330/43 [51] Int. Cl. H0ls 3/09 [58] Field ofSearch 331/945; 330/43 [56] References Cited OTHER PUBLICATIONS Willettet al., Gas Lasers at Room Pressure, Laser F0- cus, Vol. 7, (June 1971),pp. 3034.

Laflamme, Double Discharge Excitation for Atmo spheric Pressure CarbonDioxide Lasers. Rev. Sci. lnstr., Vol.41, N0. 11, (Nov. 1970), pp.1,578-1,581. Tan et al., A Tea Carbon Dioxide Laser Driven by a 200KVMark Generator, Physics Letters, Vol. 38A, No. 4, (Feb. 14, 1972), pp.225-226.

Primary ExaminerWilliam L. Sikes Attorney, Agent, or FirmJohn A. Horan;F. A. Robertson; L. E. Camaham [57] ABSTRACT An apparatus for opticallypumping a transversely excited, high pressure gaseous laser system bymeans of a double electrical discharge using a capacitor-bank networkand electronic circuitry for implementing the method. Laser energy pulseoutputs of approximately 17 Joules/liter at efficiencies of 24% havebeen obtained by the inventive concept.

8 Claims, 9 Drawing Figures PATENTED 51374 SHEET 10F 3 PATENTEBMAR 51974SHEEI 3 [1F 3 51 T so 17" 53 5:1-

LASER HEAD MARX BANK LASER HEAD APPARATUS FOR PUMPING A HIGH PRESSURELASER SYSTEM BACKGROUND OF THE INVENTION The invention described hereinwas made in the course of, or under, Contract No. W-7405-ENG-48 with theUnited States Atomic Energy Commission.

This invention relates to double discharge lasers, particularly to adouble-discharge, transversely excited, high pressure gas laser system,and more particularly to an apparatus for pumping such a laser system bythe utilization of a Marx bank as the voltage source and circuitry fortime-shaping the voltage pulse across the anode, cathode, and triggerelectrode of the laser, and/or applying voltage to the cathode-triggerindependently from the cathode-anode.

The limiting parameter for high-pressure glow discharges in gases at orabove static breakeven voltages is the arc-formation time. This is thesum of the statistical and formative time lags. The statistical timelag-is the delay required for an initiating electron from any source toappear in the discharge gap while the voltage is being applied. Thistime lag can be reduced by irradiating the gap with electrons orultraviolet radiation. Some of the other factors that affect thestatistical time delay are discharge volume, electrode surfacecondition, and profile. The time necessary for the are discharge topropagate across the gap after the discharge is initiated is called theformative time lag. Depending on the degree of the over-voltage acrossthe gap, the formative time lag can vary from less than seconds to morethan 10' seconds. For air at atmospheric pressure, the formative time isapproximately 10 seconds for'plane electrodes 0.2 cm apart at 50 percentovervoltage. The statistical time lag in this case is about 10' seconds.

Glow-discharge can be obtained in any gas between two electrodes bymaking the discharge time short compared to the arc formation time or bylimiting the discharge current density enough to prevent the formationof a constricted are. All the known transversely ex cited atmosphericpressure (TEA) CO laser techniques operate on one or both of theseprinciples.

To operate a system in the short discharge regime, it is necessary tohave a very low-inductance electrical circuit, fast switching, goodelectrode surface condition and design, e.g., Rogowski profile describedin Arch. Elektrotech 12, 1 (1923). To delay the arc formation as long aspossible, the electrodes must be uniformly spaced and well polished toeliminate burrs. Furthermore, it has been found that the fast dischargetime does not correspond to the most efficient pumping rate for COlasers. Thus, in addition to the difficulties mentioned above, theefficiency of these devices can be expected to be lower than thoseoperating in the long discharge-time regime.

The discharge-current density can be limited by either constraining thetotal current flow or by maximizing the discharge area. A row of 1,000ohm resistors to limit the discharge current in a pin-to-bar electrodeconfiguration to pump a TEA CO laser, see article by A. J. Beaulieu,Applied Physics Letters 16, 504 1970). Since the shape of a pin-bardischarge is approximately conical, the current density in this volumecannot be constant. The pumping efficiency, therefore, will vary as afunction of position. In addition, because of the energy loss in theresistors, the efficiency is low.

To enlarge the discharge area, other researches, see article byLamberton et a1, Electronics Letters 7, 141 (1971), have applied theidea of ultraviolet illumination from a nearby arc to initiate theuniform discharge between two electrodes in a TEA CO laser, by placing afine wire near two electrodes, shaped like the abovereferenced Rogowskiselectrode, with the are discharge being initiated between the wire andthe anode to generate the necessary ultraviolet radiation to trigger theglow discharge between the main electrodes. Since the duration of theultraviolet radiation is short and the intensity low, the main dischargecannot be expected to operate in the glow discharge regime for anextended period, more than a few hundred nanoseconds. Thus, this type ofdevice therefor inherits the disadvantages of the systems that operatein the shortdischarge-time regime.

The use of a corona discharge to trigger the breakdown of a gap wasfirst studied by Wynn-Williams, Phil. Mag. 1, 353 (1926). This idea hasbeen independently applied by Laflamme, Review of Scientific Instruments41, 578 (1970), and by Dumanchin et al, Laser Focus 7, 32 (Aug. 1971),to maximize the uniform discharge area in TEA CO lasers. Triggerdischarges were used to generate a uniform ionization layer near thecathode before the onset of the main discharge, a low inductance pulsetransformer electronic system being utilized as the voltage source.

SUMMARY OF THE INVENTION The present invention is directed to adoubledischarge laser generally similar in electrode geometry to that ofthe above-referenced Dumanchin et al device but differing in the voltagesource and electronic circuitry. The present invention utilizes a Marxbank (capacitor-bank network) as the voltage source and 7 electriccircuitry for time-shaping the voltage pulse across the anode, cathode,and trigger electrode of the laser instead of the low inductance pulsetransformer electronic system of the prior device, thereby substantiallyincreasing the efficiency over the prior art double-discharge lasersystems. In addition the invention provides circuitry for applyingvoltage to the cathodetrigger independently from the cathode-anode. Forexample, laser energy pulse outputs of approximately 17 Joules/liter atefficiencies of 24 percent have been reliably obtained with theinventive system, compared to a maximum 17 percent efficiency of theprior known system.

Therefore, it is an object of this invention to provide adouble-discharge, transversely excited, high pressure gas laser system.

A further object of the invention is to provide a double-discharge lasersystem which utilizes a capacitor discharge power supply and electroniccircuitry for shaping the voltage pulse.

Another object of the invention is to provide a double-discharge, highpressure gas laser system producing very high energy laser pulses athigh efficiencies.

Other objects of the invention will become readily apparent from thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates anembodiment of a double-discharge TEA CO laser utilizing a Marx bankpower supply and time-shaping circuitry;

FIG. 2 diagrammatically illustrates the electrode geometry of the FIG. 1embodiment;

FIG. 3 is a perspective view, with portions removed of adouble-discharge laser illustrating a structural embodiment of the FIG.I double-discharge laser;

FIG. 4 is an enlarged view of a portion of the FIG. 3 electrodestructure;

FIGS. 5 and 6 schematically illustrate embodiments of the Marx bankpower supplies of FIGS. 6 and 7;

FIG. 7 schematically illustrates circuitry utilized to delay applicationof voltage between cathode and anode with respect to application ofvoltage between cathode and trigger;

FIGS. 8 and 9 schematically illustrate other embodiments of theelectronic circuitry in accordance with the invention.

DESCRIPTION OF THE INVENTION In CO lasers, as pointed out above,population inversion (pumping) is accomplished by glow discharge.Ultraviolet illumination, electron-beam ionization, and corona dischargehave been used to create the initial charges needed to trigger glowdischarges in CO lasers. While the ultraviolet-illumination (UV)technique is simple and compact, the applicability of such to largesystems is questionable because of the difficulties involved inproducing intense UV radiation for extended periods. The electron-beamtechnique allows great flexibility in the density of the triggerelectrons and in the discharge duration, but these advantages must bebalanced out with the complexity associated with the use of anelectron-beam gun. The coronadischarge initiation, utilized in thisinvention, has some of the advantages of the UV and electron-beaminitiation techniques without the associated limitations andcomplexities.

A transversely excited atmospheric pressure doubledischarge laserutilizes three electrodes with two different discharges taking place inthe three-electrode system, and thus is referred to as adouble-discharge TEA CO laser. Prior to the present invention, the onlysuccessful double-discharge laser had been driven by a transformer, aspointed out above. Driving the laser directly with a single-capacitor orMarx bank provides a superior method which is simpler, more flexible,and more efficient than transformers. In addition to the low inductanceand small energy leakage, the Marx bank system does not have to dealwith the hysteresis effect in the transformers iron core, which isnecessary to insure high coupling coefficient and lower energy leakage.Combining the Marx bank power supply with circuitry for time-shaping thevoltage pulse impressed across the cathode, anode, and triggerelectrodes provide a substantial advance in the double-discharge lasersystems by providing reliable operation at high output energies over alarge volume.

Referring now to the drawings, FIG. 1 schematically illustrates anembodiment of a double-discharge TEA laser which comprises a dischargetube or vessel 10 containing a gaseous lasing medium such as a mixtureof helium, carbon dioxide, and nitrogen gases which are supplied fromseparate supply tanks and mixed prior to being introduced into vessel 10via a gas inlet 11 and discharged therefrom via a gas outlet 12. Vessel10 is provided with windows 13 and 14 positioned at the Brewster angle,and made of NaCl, for example. Positioned in spaced relation withrespect to window 13 is a reflective member 15, such as a partially(5060 percent) reflecting fiat germanium output mirror, while areflective member 16, such as a gold, I00 percent refleeting mirror witha 5-1 0 m radius of curvature, is positioned in spaced relation withrespect to window 14-, thereby defining an optical resonant cavity. Theelectrical system generally comprises a Marx bank or capacitor dischargepower supply 17 connected via electronic circuitry generally indicatedat 18 to the electrode structure, consisting of cathode means, anodemeans and trigger electrode means, within vessel 10, as described withrespect to FIGS. 2-4, the circuitry 18 being described in detail withrespect to FIGS. 7-9, with a more detailed description of the Marx bankI7 being set forth with respect to FIGS. 5 and 6. While the FIG. 1embodiment is illustrated in an oscillator configuration, it can beutilized as efficiently in an amplifier configuration as known in theart.

FIG. 2 diagrammatically illustrates the electrode structure of the FIG.1 double-discharge laser, while FIGS. 3 and 4 show a structuralembodiment thereof. As seen in FIG. 2, the vessel 10 includes wall orside sections 19 and bottom or plate member 20, constructed of materialsuch as acrylic Lucite. A cathode assembly generally indicated at 21 ismounted in spaced relation with bottom member 20 on supports 22. Atrigger electrode assembly generally indicated at 23 extends throughbottom member 20 and adjacent the cathode assembly 21, as described ingreater detail hereinafter with respect to FIGS. 3 and 4. An anode 24 ismounted in spaced relation with respect to cathode assembly 21 andsecured in wall sections 19 of vessel 10 forming the top or closuremember defining in vessel 10 a chamber or gas enclosure 25 whichcontains the gaseous lasing media.

Referring now to the mechanical construction details of an embodiment ofthe double-discharge laser, as shown in FIGS. 3 and 4, vessel 10additionally includes end sections 26 having portholes in which aremounted tube-like members 27, the outer end of which are secured theBrewster angle windows 13 and 14, defining an optical path indicated bythe double arrow 28. The cathode assembly 21, in this embodiment,consists of 21 0.039 cm thick aluminum alloy strips 29 milled to 1.8 cmwide and 92 cm long. The ends 30 of strips 29 are semicircular, with aradius of 0.9 cm. Care is taken to ensure a smooth transition betweenthe straight and semicircular sections of the strips 29. The strips 29are held together near both ends (only one shown) and at the middle (notshown) by 0.316 cm diameter aluminum tie rods 31. Ring spacers (notshown) with 0.316 cm i.d., 0.633 cm o.d., and 0.600 t 0.002 cm thicknessare placed on the tie rods 31 intermediate the strips 29 to keep thestrips about 6 mm apart. The strips 29 are assembled such that the topedges are coplanar and the tie rods 31 supported in members 22 (see FIG.2).

The gas enclosure or chamber 25 in the FIG. 3 embodiment is 17 cm wideand 106 cm long, with the side wall sections 19 of vessel 10 being 1.9cm thick, the bottom member 20 being 3.175 cm thick, and the endsections 26 being 2.53 cm thick Lucite. The portholes in which tube-likemembers 27 are mounted have a diameter of 3.16 cm. No effort was takento make the chamber 25 vacuum tight since the lasing medium is atatmospheric pressure. Slots 32 (see FIG. 2), 0.4 cm by 0.4 cm, were cutalong the full length of the side wall sections 19 of the vessel tosupport the anode 24, nylon screws via holes in wall sections 19 (notshown) secure the anode in slots 32.

The anode 24 in the FIG. 3 embodiment comprises an aluminum plate 17.8cm wide, 0.316 cm thick, and 106 cm long and is positioned such that theside (inner side) facing the cathode assembly 21 is 5 cm from the top ofthe cathode strips 29. All of the edges of the anode 24 are rounded toprevent large field gradients. Care was taken in cutting the slots 32 onthe side walls 19, tapping holes for the nylon screws, and constructingthe cathode assembly supports 22 so that the height variation in the 5cm discharge gap between anode and cathode is not more than 0.01 cm.

The trigger electrode assembly 23 comprises, in the FIG. 3 embodiment,twenty trigger electrodes 33, each made from 56 mm Pyrex capillary glasstubes 34 through which Nichrome wires 35 extend. The outside diameter ofthe capillary tubes 34 varied between 0.550 and 0.560 cm. The tubes 34were sealed at one end (not shown) and include a 90 bend 36 near theopen other end. The distance from the sealed end to the 90 bend 36 is100 i 0.5 cm and 10 i 0.5 cm from the bend 36 to the open end. The tubes34 are supported and clamped near the sealed end and near the bend 36,by means not shown and are each positioned intermediate a pair ofcathode strips 29 so that the 0.025 cm Nichrome wires 35 are at the samelevel as the top edge of the aluminum cathode strips 29. It is importantto have the glass tubes 34 tightly secured since they vibrate during thedischarge. Since the tubes 34 tend to sag, small plastic blocks (notshown) are placed near the center to support them. The Nichrome wires 35are clamped to a copper bus bar 37 which is connected to groundindicated at 38 through a 6,000 pF capacitor 39, as generallyillustrated in FIG. 1 and described hereinafter with respect to FIG. 7.

As pointed out above, a gaseous lasing media such as helium, carbondioxide, and nitrogen gases (He/- Co /N in a ratio of 5:111, which comefrom separate supply tanks are mixed in a flow meter mixer, not shown,before being introduced into the gas enclosure or chamber 25.

The electrical construction embodiments of the Marx bank 17 of FIG. 1are illustrated in FIGS. 5 and 6. In the FIG. 5 embodiment the Marx bank17' is constructed in a coaxial configuration with two 30 kV, 0.5 pFcapacitors 40 and 41. Each capacitor has an internal inductance of 0.05.|.H, and all the connections in the Marx bank embodiments are made with7.5 cm

wide copper sheets. The inductance of the Marx bank 17' as a whole isapproximately 0.2 pH. The capacitors 40 and 41 are charged by anunregulated negative high voltage (30 kV, for example) power supply 42via 10 Meg resistors 43 and 44, and two trigger spark gap assemblies 45and 46 are used to switch the stored energy. Capacitors 40 and 41 areconnected via 10 Meg resistors 47 and 48 to ground indicated at 49.

The capacitor bank 17" illustrated in FIG. 6 comprises a single 60 kV,0.25 uF capacitor 50 charged by a negative high voltage (-HV) powersupply 42' via a 10 Meg resistor 51, and provided with a trigger sparkgap 52, while being connected to ground as indicated at 53. Thus, theenergy source for the laser may be a capacitor network as in FIG. 5 or asingle capacitor as in FIG. 6.

In the embodiment of the invention as illustrated, the capacitancebetween the cathode assembly 21 and the Nichrome wires 35 was measuredto be 560 1: 7 pF, while a capacitance of i 5 pF was measured betweenthe cathode assembly 21 and anode 24.

During testing of the invention, the high voltage was measured with a1,000:l resistive divider made from carbon resistors. The currents weremeasured by two current-viewing resistors. A liquid-nitrogen-cooled,gold-doped Ge detector was used to detect the pulse shape of the 10.6 p.laser radiation. All the signals were displayed on an oscilloscope. Theenergy output was measured by a ballistic thermopile coupled to anenergy meter and a chart recorder.

FIG. 7 illustrates a circuit used in the rise time measurementsconducted on the inventive concept, wherein a high voltage was impressedon the trigger discharge and the main discharge at different times. Thecircuitry is connected to a laser head or vessel 10 having a cathodeassembly lead 21 a trigger assembly lead 23', and an anode lead 24.Cathode lead 21 is connected to a Marx bank l7-and via an electricallead 54 to a trigger timing mechanism 55 which in turn is electricallyconnected via lead 56 to a spark gap assembly 57. A first capacitor 58is mounted via leads 59 and 60 intermediate anode lead 24 and lead 54,while a second, but smaller capacitor 61 is mounted betweentrigger lead23 and a lead 62 connected to ground as indicated at 62, one leg ofspark gap 57 being connected to lead 59 with the other leg connected toground lead 62. Anode lead 24 is connected via a resistor 63 to groundlead 62 while Marx bank 17 is connected via lead 64 to ground lead 62.Thus by the addition of the trigger timing mechanism 55 and the sparkgap assembly 57 high voltage from Marx bank 17 was impressed on thetrigger discharge (between trigger assembly 23 and cathode assembly 21)and the main discharge (be tween cathode assembly 21 and anode 24) atdifferent times. In these rise time measurement tests it was determinedthat the best operation was obtained when the main discharge wasinitiated approximately 2 usec after the trigger discharge.

The trigger discharge depends on the corona discharge from the sharpedges of the cathode strips 29. The corona current depends upon thecurvature of the edges and the proximity of the glass tubes. The coronacurrent from the cathode assembly has been determined by calculations.At 60 kV an average corona current of 36.6A is obtainable, and using themeasured capacitance of 560 pF between the cathode and trigger wires 35,a charging time of 0.9 usec is obtained. Similarly, an average currentof 12.8A and a charging time of approximately 1.3 usec is obtained at 30kV. When the finite high voltage rise time and losses are taken intoaccount, a charging time of approximately 2 usec is obtained. Thus, the2 usec measurement corresponds to the calculated time necessary to allowthe trigger discharge to build up to the maximum pre-ionization chargedensity that the circuit allows.

If the circuit does not contain spark gaps external to the Marx bank(spark gap 57), then a delay time must be introduced by other means. Forexample, in the circuits described hereinafter with respect to FIGS. 8and 9, the voltage rise is regulated by the LC values. The optimum risetime was also found to be approximately 2 usec under a wide range ofoperating conditions.

Once the pre-ionizing charges are dissipated, are formation follows. Itis therefore imperative that the high voltage be reduced below thebreakdown voltage shortly after the peak of the main current pulse.However, the glow discharge should be maintained as long as possible,since more laser output results from the longer pumping time. Thus, forbest operation, the high voltage should be brought down enough that noarcing occurs and at the same time be high enough to extend the pumpingtime.

In the course of testing to verify the invention, the double-dischargelaser was operated with numerous different circuits containingresistors, capacitors, inductors, and spark gaps. Circuits containingspark gaps external to the Marx bank, as illustrated by the FIG. 7embodiment, that were programmed to fire at a predetermined time werefound to be sensitive to changes in operating conditions, and thus thiscircuit was found to be not as effective as, for example, the typesillustrated in FIGS. 8 and 9. While the FIG. 7 circuit showed thissensitivity, this need not be the case for all independent firingcircuits. I

It is important to note that although the rise and fall time criteriawere followed in the testing efforts, some circuits did not give theexpected performance. The parameter that was varied with these circuitswas the slope of the high voltage pulse near the beginning. When thevoltage pulse rose rapidly, a sharp current pulse was observed, with afull width at the base of less than 0.5 usec, in the trigger dischargeand no main discharge current until arcing occurred. Even when thearcing in the main gap occurred several microseconds after the start ofthe voltage pulse, no corona current was observed in the trigger gapafter the initial spike. The performance of the double-discharge laserimproved when the initial slope of the voltage pulse was decreased. Inthat case, a slow-rising trigger discharge current was observed, whichcontinued for about 2 ,usec without the initial spike, and a large maindischarge current. Thus, in addition to the rise and fall timerequirements, the initial slope of the high-voltage pulse must be keptsmall.

A uniform glow discharge over the entire 5 l2 92 cm discharge volume ofthe FIG. 3 embodiment was obtained with the circuits of FIGS. 8 and 9.These circuits gave reliable performance under all operating conditions.

Referring now to the FIG. 8 embodiment, a laser cavity or head 10containing a gaseous lasing media provided as in the FIG. 7 embodimentwith a cathode lead 21', a trigger lead 23 and an anode lead 24, cathodelead 21 being connected to a Marx bank C via an inductance coil L,;trigger lead 23' being connected through a capacitor 61, such as a 6,000pF type, to ground via lead 62; and anode lead 24 being connecteddirectly to ground lead 62, with Marx bank C, being connected to groundvia lead 64. A capacitor C is connected on one side to cathode lead 21intermediate inductance coil L, and laser head 10', and on the otherside to ground lead 62, while a resistor R, is connected at one sideintermediate inductance coil L, and Marx bank C, and on the other sideto ground lead 62.

The FIG. 9 embodiment is generally similar to that of FIG. 8 exceptresistor R, has been eliminated and a capacitor C positioned in anodelead 24' with a resistor R connected on one side to anode lead 24intermediate capacitor C and laser head 10, and on the other side toground lead 62. The Marx bank C, in FIGS. 8 and 9 may be constructed,for example, as illustrated in FIGS. 5 and 6.

The value of the L,C combination, as mentioned above, is chosen to giveapproximately 2 usec of rise time. For example, L, is 15 [LH and C is0.05 uF. Changing L, and C showed that a 25 percent variation in therise time did not significantly affect the operation. Also, the locationof the inductor L, is important. When it is placed too close the lasercavity, the high magnetic field can introduce distortions in theelectric field and cause arcing.

R, and C R are chosen so that the time constants for C,R, and C 11,, areapproximately 10 usec. This ensured the proper drop in the high voltagediscussed earlier. It was found that the high voltage across the maingap (cathode-anode) must be reduced to and kept below approximately 25kV shortly after the peak of the current pulse. This caused a lowdischarge current to flow across the main gap for several moremicroseconds. This current flow has, in some cases, increased the laseroutput by approximately 50 percent.

In the tests conducted, the best operation was obtained utilizing theFIG. 8 circuit with resistor R, 40 Q. When R, was increased above thisvalue by about 25 percent, the system frequently arced. On the otherhand, when the resistor value was decreased, the laser energy outputefficiency dropped. It should be noted that, in the FIG. 8 circuit withthe above given values, even relatively severe electrode damages did notproduce arcing. While testing of the FIG. 9 circuit has not, at thistime, been as extensive as on the FIG. 8 embodiment, the tests thus farconducted indicate that this circuit will perform even more efficiently.

Using the circuit of FIG. 8, the disclosed doubledischarge laser hasbeen operated with He/CO /N gaseous lasing mixtures in ratio rangingfrom 10:1 :1 to 3:121, respectively, at voltages between 45 and 64 kV.In all cases, air sparks inside the thermopile cone was obtained. Atypical laser output of about 17 J/liter was obtained which isequivalent to an efficiency of 24 percent. The best energy output perunit volume and the corresponding efficiency of the prior knowndoubledischarge laser systems varied from 5.49 to 18 J/liter and 4.5 to17.4 percent efficiency, thus present invention has provided asubstantial advance in the energy output per unit volume and thecorresponding efficiency. With the present invention, the pulseJo-pulsevariation in the output energy was less than 10 percent, which is duepartly to the voltage variation in the unregulated power supply used inthe testing. The best performance of the inventive system, in anoscillator configuration, was obtained with a 5:1:1 gas mixture at 56kV, using flat gold and 50-60 percent reflecting Ge mirrors, asillustrated in FIG. 1, with 5 m radii of curvature. In addition to theabove-mentioned tests, oscilloscope traces were made of the voltage,main current, trigger current, and laser pulse shape to further verifythe advance provided by the invention.

It has thus been shown that the present invention provides a means forreliably and efficiently obtaining high energy laser pulses from atransversely-excited, high presure a 1 atm) gas laser system usingdouble electrical discharge optical pumping which incorporates a Marxbank (capacitor discharge) as a voltage source and electronic circuitryfor time-shaping the voltage pulse across the anode and cathode of thelaser as well as applying the voltage to the cathode-triggerindependently from the cathode-anode circuit, thus comprising asubstantial advance over the prior known systems using a low inductancepulse transformer electronic system.

While particular embodiments of the invention have been illustrated anddescribed, modifications will become apparent to those skilled in theart, and it is intended to cover in the appended claims all suchmodifications as come within the spirit and scope of the invention.

What we claim is:

1. In a double-discharge laser system including vessel means forcontaining a gaseous lasing media and within which are positionedelectrode means consisting of cathode means, trigger electrode means,and anode means for exciting the media to a lasing state, theimprovement comprising: a capacitor discharge power supply meansoperatively connected to said electrode means for impressing electricaldischarges thereacross, and electronic circuitry operativelyinterconnected between said power supply means and said electrode meansfor time-shaping the discharge across said cathode means and said anodemeans and/or for independently applying voltage between said cathodemeans and said trigger electrode means, and between said cathode meansand said anode means, said electronic circuitry including cathode leadmeans electrically in terconnecting said power supply means and saidcathode means through inductor means, trigger electrode lead meanselectrically connecting said trigger electrode means to ground through afirst capacitor means, anode lead means operatively connecting saidanode means to ground, means for electrically connecting said powersupply means to ground, and second capacitor means electricallyconnected on one side thereof to said cathode lead means intermediatesaid inductor means and said cathode means and on the other side thereofto ground.

2. The laser system defined in claim 1, wherein said capacitor dischargepower supply means comprises at least a plurality of capacitors, a highvoltage means for charging said capacitors, resistor means electricallyconnected intermediate said capacitors and said high voltage means,resistor means electrically connected intermediate said capacitors andground, and trigger means electrically connected to said capacitors forswitching energy stored in said capacitors to said electrode means.

3. The laser system defined in claim 2, wherein said trigger meanscomprises a plurality of spark gap assemblies, each one of which beingoperatively connected to an associated one of said plurality ofcapacitors.

4. The laser system defined in claim 1, wherein said capacitor dischargepower supply means comprises a single capacitor electrically connectedto a high voltage means for charging same, resistor means electricallyconnected intermediate one side of said capacitor and said high voltagemeans, means electrically connecting another side of said capacitor toground, and trigger means electrically connected to said capacitor forswitching energy stored therein to said electrode means.

5. The laser system defined in claim 1, additionally including resistormeans electrically connected on one side thereof to said cathode leadmeans intermediate said power supply means and said inductor means andon the other side thereof to ground.

6. The laser system defined in claim 1, additionally including a thirdcapacitor means electrically connected to said anode lead meansintermediate said anode means and ground, and resistor meanselectrically connected on one side thereof to said anode lead meansintermediate said anode means and said third capacitor means and on theother side thereof to ground.

7. The laser system defined inclaim 1, wherein said cathode meanscomprises a plurality of cathode strips supported in spaced relationshipand having the upper surface of each of said spaced strips in alignment,wherein said trigger electrode means comprises a plurality of triggerelectrodes each positioned intermediate a pair of said cathode stripsand in alignment with said upper surface of said cathode strips, andwherein said anode means comprises a plate-like member mounted above andin spaced relation with respect to said cathode strips and said triggerelectrodes.

8. The laser system defined in claim 7, wherein said cathode strips eachcomprises a longitudinally extending body portion and curved endportions, wherein said trigger electrodes each comprises a wire-likemember surrounded by a tube-like means, said plurality of triggerelectrodes extending outwardly through said vessel means and each ofsaid wire-like members being electrically connected to a bus bar means.

1. In a double-discharge laser system including vessel means forcontaining a gaseous lasing media and within which are positionedelectrode means consisting of cathode means, trigger electrode means,and anode means for exciting the media to a lasing state, theimprovement comprising: a capacitor discharge power supply meansoperatively connected to said electrode means for impressing electricaldischarges thereacross, and electronic circuitry operativelyinterconnected between said power supply means and said electrode meansfor time-shaping the discharge across said cathode means and said anodemeans and/or for independently applying voltage between said cathodemeans and said trigger electrode means, and between said cathode meansand said anode means, said electronic circuitry including cathode leadmeans electrically interconnecting said power supply means and saidcathode means through inductor means, trigger electrode lead meanselectrically connecting said trigger electrode means to ground through afirst capacitor means, anode lead means operatively connecting saidanode means to ground, means for electrically connecting said powersupply means to ground, and second capacitor means electricallyconnected on one side thereof to said cathode lead means intermediatesaid iNductor means and said cathode means and on the other side thereofto ground.
 2. The laser system defined in claim 1, wherein saidcapacitor discharge power supply means comprises at least a plurality ofcapacitors, a high voltage means for charging said capacitors, resistormeans electrically connected intermediate said capacitors and said highvoltage means, resistor means electrically connected intermediate saidcapacitors and ground, and trigger means electrically connected to saidcapacitors for switching energy stored in said capacitors to saidelectrode means.
 3. The laser system defined in claim 2, wherein saidtrigger means comprises a plurality of spark gap assemblies, each one ofwhich being operatively connected to an associated one of said pluralityof capacitors.
 4. The laser system defined in claim 1, wherein saidcapacitor discharge power supply means comprises a single capacitorelectrically connected to a high voltage means for charging same,resistor means electrically connected intermediate one side of saidcapacitor and said high voltage means, means electrically connectinganother side of said capacitor to ground, and trigger means electricallyconnected to said capacitor for switching energy stored therein to saidelectrode means.
 5. The laser system defined in claim 1, additionallyincluding resistor means electrically connected on one side thereof tosaid cathode lead means intermediate said power supply means and saidinductor means and on the other side thereof to ground.
 6. The lasersystem defined in claim 1, additionally including a third capacitormeans electrically connected to said anode lead means intermediate saidanode means and ground, and resistor means electrically connected on oneside thereof to said anode lead means intermediate said anode means andsaid third capacitor means and on the other side thereof to ground. 7.The laser system defined in claim 1, wherein said cathode meanscomprises a plurality of cathode strips supported in spaced relationshipand having the upper surface of each of said spaced strips in alignment,wherein said trigger electrode means comprises a plurality of triggerelectrodes each positioned intermediate a pair of said cathode stripsand in alignment with said upper surface of said cathode strips, andwherein said anode means comprises a plate-like member mounted above andin spaced relation with respect to said cathode strips and said triggerelectrodes.
 8. The laser system defined in claim 7, wherein said cathodestrips each comprises a longitudinally extending body portion and curvedend portions, wherein said trigger electrodes each comprises a wire-likemember surrounded by a tube-like means, said plurality of triggerelectrodes extending outwardly through said vessel means and each ofsaid wire-like members being electrically connected to a bus bar means.